Association between smoking habits and dental care utilization and cost using administrative claims database and specific medical check-up data

Background This study aims to evaluate the association between smoking habits and dental care utilization and cost in individuals registered with the Japan Health Insurance Association, Osaka branch. Methods We used the administrative claims database and specific medical check-up data and included 226,359 participants, who visited dental institutions, underwent dental examinations, and underwent specific medical checkups, with smoking data from April 2016 to March 2017. We calculated propensity scores with age, gender, exercise, eating habits, alcohol intake, and sleep. We also compared dental care utilization with the total cost of each procedure. Results According to propensity score matching, 62,692 participants were selected for each group. Compared to non-smokers, smokers were younger, and a higher proportion were men. Smokers tended to skip breakfast, have dinner just before bed, and drink alcohol. After adjusting for potential confounding factors with propensity score matching, the mean annual dental cost among smokers was significantly higher than non-smokers. The prevalence of pulpitis, missing teeth, and apical periodontitis were higher among smokers than non-smokers, while inlay detachment, caries, and dentine hypersensitivity were higher among non-smokers. Conclusion This study suggests that smokers have higher dental cost consisted of progressive dental caries, missing teeth, and uncontrolled acute inflammation that necessitated the use of medications. It is suggested that smokers tend to visit the dentist after their symptoms become severe.


Introduction
According to the National Health and Nutrition Survey in 2017, the overall prevalence of smoking in Japan is 17.8% (29.0% among men and 8.1% among women)1. Tobacco smoking is still one of the leading causes of mortality and morbidity worldwide2. Smoking is not only the cause of lung cancer but also a risk factor for various dental diseases such as periodontal disease, oral cancer, caries, and tooth loss, as indicated by several epidemiologic studies3 -6 . Drilea et al. reported that smokers were less likely to visit dental clinics than non-smokers, when the data were adjusted for age, sex, race/ethnicity, poverty level, dental insurance, and dentate status7. As a result, they are more susceptible to oral problems such as dentine hypersensitivity, toothache, and orofacial pain8. Another study showed that smokers were more likely to perceive that they had poorer oral health and tended to undergo dental checkups only when symptomatic9. Moreover, lower use of dental service among smokers increased the risk of several oral diseases including oral cancer10. The use of dental services after the appearance of symptoms is associated with higher dental costs. Studies of the healthcare costs among smokers have received attention from researchers. Ide et al. reported that smoking could be the cause of increased dental care utilization and cost through the deterioration of oral health11. Based on a cohort study in Finland, current smokers were more likely to use healthcare services and visit a dentist with increased healthcare costs than never-smokers12. Expenditure associated with smoking includes not only direct dental costs but also indirect costs such as loss of time spent on travel and treatment with lost work time13. Some factors were associated with dental care utilization, such as characteristics, health beliefs, financial resources, and access to health insurance14.
In the Japanese medical insurance system, all Japanese residents enroll in an insurance group depending on the individual's age and occupation15. The healthcare system includes Employees' Health Insurance, which covers employees of private companies and their families16. Those who work for small and medium-sized enterprises and their families are members of the National Health Insurance Association. Under the Japanese free access healthcare system, individuals can consult multiple medical institutions, including dental clinics and hospitals17. All insured people and their dependents over 40-74 years can undergo specific health checkups and receive health guidance every year. From 2008, health checkups to prevent metabolic syndrome have been conducted, according to the recommendations of the Health and Medical Service Law for the Aged18. They provide valuable information, such as smoking status, to prevent non-communicable diseases.
Little research has been conducted on dental care utilization and cost using the Japanese administrative claims database. This study aims to evaluate the association between smoking habits and dental care utilization and cost among participants registered with the Japan Health Insurance Association, Osaka branch.

Data source
A cross-sectional study was conducted using data from the administrative claims database and specific check-up data obtained from the Japan Health Insurance Association, Osaka branch. The population in the Japan Health Insurance Association covers almost 40 million people; it is the largest medical insurer in Japan. A member firm of the Osaka Branch is a small-or medium-sized business with several small offices; approximately 80% of the offices have fewer than nine employees. The study participants were collected from April 2016 to March 2017. The participants aged older than 20 years, individuals with specific check-up records, and at least one dentist visit were included. The exclusion criteria were as follows: individuals who had missing data in the questionnaire regarding specific check-up and those whose questionnaire about smoking had answers that differed from the doctor's interview. A flow diagram of the study participants is shown in Fig. 1. Of the 1,621,252 individuals from the database of the Japan Health Insurance Association, Osaka branch, our final analytic sample consisted of 226,359 participants (from April 2016 to March 2017). Among them, 29.0% were smokers.

Questionnaire and clinical parameters in specific medical checkup
The smoking status was determined during the medical consultation. Moreover, we also took into consideration the participant's answer about smoking status. The questionnaire included the question, "Currently, do you smoke habitually?" (Yes/No). Currently habitual smokers were "those who have smoked a total of 100 or more cigarettes, or 6 months or longer, and have smoked in the last month. " Information of medication (hypotensive, insulin or hypoglycemic, hyperlipidemia drugs) and medical history (stroke, heart disease, chronic renal failure or artificial dialysis, anemia and metabolic syndrome) were obtained from the personal questionnaire. Further, we included other items, such as the following questions: "Have you gained over 10 kg from your weight at age 20?" (Yes/No); "Are you in the habit of exercising to sweat lightly for over 30 min a time, 2 times weekly, for over a year?" (Yes/No); "In your daily life, do you walk or do an equivalent amount of physical activity more than one hour a day?" (Yes/No); "Is your walking speed faster than the speed of those of your age and sex?" (Yes/No); "Have you gained or lost over 3 kg from your weight in a year?" (Yes/No); "Is your eating speed faster than others?" (Fast/ Normal/ Slow); "Do you skip breakfast more than 3 times a week?" (Yes/No); "Do you have any snacks or sweet beverages after dinner more than 3 times a week?" (Yes/No); "Do you have an evening meal within 2 h before bedtime more than 3 times a week?" (Yes/No); "How often do you drink alcohol?" (Everyday/ Sometimes/ Rarely); and "Do you feel refreshed after a night's sleep?" (Yes/No). Furthermore, the check-up variables included waist circumstance (WC), body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol, triglycerides, high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), fasting blood glucose (FBG), HbA1c, glutamic-oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), ɤ-glutamyl transpeptidase (ɤ-GTP), uric acid (UA), and estimated glomerular filtration rate (eGFR).

Dental and medical utilization and cost
The data were linked with the claims database file using participants' ID numbers. We also calculated dental and medical care utilization using the total annual cost of each procedure from April 2016 to March 2017. The annual number of medical visits was calculated for each participant. We counted the number of all diagnosed diseases and procedure codes of each group and calculated the prevalence between smokers and non-smokers.

Propensity score matching and statistical analysis
We calculated propensity score, defined as the conditional probability of each participant having a smoking habit given several confounders, such as age, sex, exercise, physical activity, walking speed, eating habit (speed, breakfast, snacks, and evening meal), alcohol intake, and sleep using logistic regression (Table 1). Standardized differences were calculated to assess the balance of covariates between smokers and non-smokers. If the standardized differences were less than 10%, the covariates were considered balanced19. The propensity score of the smoking group and the non-smoking group were compared to create matched pairs (smokers and non-smokers as reference) within a 0.15 caliper. In this propensity score model, goodness of fit was secured (C-index was 0.699). The Student's t-tests and   Table 2 shows the characteristics of smokers and nonsmokers before and after propensity score matching. Compared to non-smokers, smokers were younger, and a higher proportion were men. The prevalence of anemia was higher in non-smokers (5.5% in smokers versus 10.0% in non-smokers). The results also indicate the differences in lifestyle between smokers and non-smokers.

Demographic and clinical characteristics of participants
Smokers tend to skip breakfast, have dinner just before bed, and drink alcohol. Metabolic syndrome participants were 15.8% in smokers and 12.7% in non-smokers. According to propensity score matching, 62,692 participants were selected for each group. The two groups became well-balanced after propensity score matching according to standardized differences (bold letter). Clinical parameters and applicable metabolic syndrome are shown in Table 3. Smokers had a larger WC, triglyceride, ɤ-GTP and eGFR, and lower levels of total cholesterol and HDL. Standardized differences were higher than 0.1 in SBP, DBP, total cholesterol, triglyceride, HDL, and eGFR. However, the rate of metabolic syndrome was well-balanced between the two groups.

Dental and medical care utilization and cost between smokers and non-smokers
As shown in Table 4, after adjusting for potential confounding factors with propensity score matching, the mean annual dental cost was 54,520 JPY (Standard deviation (SD): 54,774) among smokers, significantly higher than non-smokers (47,944 JPY; SD: 50,951) (P < 0.001). Of the 125,384 participants, 19.0% of the smokers and 13.6% of the non-smokers did not visit medical institutions. Non-smokers tend to see medical doctors with higher medical cost.

Dental diagnosis and dental procedure between smokers and non-smokers
Pulpitis, missing teeth, and apical periodontitis were more frequently diagnosed in smokers, while inlay detachment, dental decay, and hypersensitivity were more common in non-smokers ( Table 5). As for dental procedures, smokers needed more frequent dental recalls and medication-assisted treatment to control acute inflammation (as shown in Table 6). However, the first consultation that included the Basic Periodontal Examination and scaling procedures were more frequently coded in non-smokers.

Discussion
In the present study, we show a positive association between smoking habit and high dental cost. Smokers were more likely to incur dental care costs than nonsmokers among the users of dental and medical checkup services. Warnakulasuriya et al. have shown that oral health risk such as oral cancer, periodontal disease, tooth loss, implant failure, and dental caries have a strong association with tobacco smoking20. The cost of smoking exceeds the cost of periodontal therapy21. However, we could not obtain information about daily tooth cleaning habits, such as the frequency of using dental floss or other types of teeth cleaning tools. The result of the present study is consistent with that of a report that current smokers were less likely to consult a dentist in the past year than those who never smoked8. There was no significant association between children's exposure to secondhand smoke and dental expenditure using the Medicaid database22. It is also necessary to consider the impact of secondhand smoke on medical and dental costs. In our results, smokers were more susceptible to progressed dental caries, missing teeth, and uncontrolled acute inflammation. Therefore, the rate of recalls and need for medications to control acute dental inflammation was higher in smokers. Non-smokers were more likely to receive the first consultation, including the Basic Periodontal Examination, and the scaling procedure as part of the routine dental examination. Some reports showed that, compared with never smokers, current smokers were less likely to exercise daily preventive care8.
Based on the Act on Ensuring Medical Care for the Elderly, the Specified Health Checkup was started in 2008. In 2016, the targeted population was 53.6 million individuals with basic insurance, aged 40 to 74 years old; the total average rate of those who received this checkup was 51.4%. Although the consultation rate increased over time, the financial situation of the insurer remained variable. More than 75% of insured individuals underwent specific checkups in the health insurance society, but less than 50% of insurers received checkups in the National Insurance Association23. Individuals who have not undergone routine medical checkups are included in the list.
The data of participants in this study were derived from the administrative claims database and specific checkups. The advantage of a real-world database, such as the medical claims database used in our study, is that it can provide diagnosis and treatment information even if a participant switches to another medical institution24. Moreover, we have used a propensity score matching method to adjust for potential confounding variables, such as lifestyle between the two groups. There are some limitations to this study. We could only consider the medical and dental service under health insurance due to the characteristics of the administrative claims database. Individuals who did not visit the dental clinic were not analyzed. Therefore, medical expenses may have been overestimated. Free dental treatments, such as whitening, orthodontic treatment, implants, and aesthetic dentistry, were not included in this analysis. According to a survey conducted by the Ministry of Health, Labour and Welfare, the implementation rate of specific checkups was 47.4% in all Japan Health Insurance Associations. Hence, the utilization of medical and dental services may have been overestimated considering the total population. The information regarding pharmacy claims was not included in this database. Thus, the cost of healthcare excluded medication costs. We could not distinguish between former smokers and non-smokers without data on the smoking period. Jeong reported that electronic cigarette vaping and conventional cigarette use had a significant association with periodontal disease rates25. However, we were unable to identify the type of cigarettes used in this study. Socioeconomic status is a well-known risk indicator for dental disease26. The study population comprised insured individuals who were enrolled in the Japan Health Insurance Association, Osaka branch. However, we could not evaluate the economic situation in each household. Adults 75 years or older with high medical and dental costs could not be included in this study, as they usually transfer to the medical care system for the elderly.
According to National Health and Nutrition Survey, smoking habits are declining among both men and women since 2016 (30.2% in men and 7.2% in women). Although smokers are at a higher risk of oral pain, smoking cessation significantly decreases the risk27. The adverse effects of smoking on oral health are often reduced by smoking cessation. As there exists a strong dose-dependent association between smoking and tooth loss, dentists play a crucial role in tobacco control2.
In summary, this study suggests that smokers have higher dental costs, most often due to acute illness. Our findings support the call for public policies to promote non-smoking activities. Promoting regular dental visits is one strategy to help people prevent and treat oral disease in early stages.